Increase of dissolved inorganic carbon and decrease of pH in near surface waters of the Mediterranean Sea during the past two decades

Two three-year-long time series of hourly measurements of the fugacity of CO2 (fCO2) in the upper 10 m of the surface layer of the northwestern Mediterranean Sea have been recorded by CARIOCA sensors almost two decades apart, in 1995–1997 and 2013–2015. By combining them with alkalinity derived from measured temperature and salinity, we calculated changes of pH and dissolved inorganic carbon (DIC). DIC increased in surface seawater by ~ 25 μmol kg−1 and fCO2 by 40 μatm, whereas seawater pH decreased by ~ 0.04 (0.0021 yr−1). The DIC increase is larger than expected from equilibrium with atmospheric CO2. This supports the hypothesis of a ~ 15 % contribution of the Atlantic Ocean as a source of anthropogenic carbon to the Mediterranean Sea through the strait of Gibraltar. We estimate that the part of DIC accumulated over the last 18 years represents ~ 30 % of the total change since the beginning of the industrial period.

Merlivat L., Boutin J., Antoine D., Beaumont L., Golbol M. & Velluci V., 2017. Increase of dissolved inorganic carbon and decrease of pH in near surface waters of the Mediterranean Sea during the past two decades. Biogeosciences Discussions. Article.


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